The present invention relates generally to an apparatus or arrangement for duplicating a workpiece by scanning of a model, obtaining data from the workpiece and storing the data and transforming the data into numerical control sets for the control signals for the drive of a numerically controlled milling machine. More particularly, the present invention is directed to an arrangement for duplicating a workpiece, which performs a collision test and applies a correction movement on the milling tool in response to the collision test.
The production of workpieces with spatially curved surfaces is among the most difficult of machining problems. There has been previous efforts to improve duplicating techniques for this purpose. However, since the general introduction of numerically controlled (NC) processing machines, not very much attention has been devoted to further develop the so-called copying milling machines Only recently has there been a regained interest in the duplication of spatial models, particularly through the use of NC-technology in machines for duplicating free form surfaces which are difficult to describe mathematically.
In order for NC-controlled copying milling machines to duplicate a workpiece, a model of the workpiece is scanned by means of a measuring sensor. The measurement data which are obtained in this manner are typically stored in the digital memory of the NC-control of the machine. This is generally referred to as "digitalization of spatial models". For example, such a digitalization process is described in EP-A1-227842. Since such a digitalization process is known in the art and is not an object of the present invention, no further details of the digitalization process are given here.
The physical spatial dimensions of the elements of the duplicating arrangement usually lead to inaccurate dimensional data. For example, data that are determined by a measuring sensor as dimensional data of the workpiece are inaccurate since the sensing arm includes a measuring sensor which has physical dimensions. For example, the scanning sensor generally includes a scanning ball which has physical spatial dimensions. The tool with which the surface of the workpiece is to be generated also includes physical dimensions. The dimensions of the tool do not generally correspond to the radius of the scanning ball of the measuring sensor. These differences along with the variations between the data received in the scanning direction and the processing or working-off of the data in the processing direction by the tool must be taken into account in processing the dimensional data obtained of the model.
NC-controlled duplicating machines which perform these functions are expensive since, in addition to the NC machine, a powerful personal computer including all of the corresponding peripheral equipment is required. Such an arrangement is described in a report in the periodical "Werkzeug and Formbau" June 1987, pages 79 and 80.
Therefore, in view of the above, it is a primary object of the present invention to provide an arrangement which uses a machine tool equipped with path control for the production of workpieces, which arrangement may be used to reproduced free formed surfaces.